Index: share/man/man4/em.4
===================================================================
--- share/man/man4/em.4
+++ share/man/man4/em.4
@@ -258,6 +258,11 @@
 Defaults to 1.
 Only valid with kernel configuration
 .Cd "options EM_MULTIQUEUE".
+.It Va hw.em.max_dma
+Non-zero value that controls how many mbufs are DMA'd to and from the
+hardware and what the tso size advertized up the stack will be.  Defaults
+to EM_MAX_SCATTER or 64 and is adjusted as a quirk for other boards to a 
+value of EM_MAX_LEGACY_SCATTER or 40.
 .El
 .Sh FILES
 .Bl -tag -width /dev/led/em*
Index: sys/dev/e1000/if_em.h
===================================================================
--- sys/dev/e1000/if_em.h
+++ sys/dev/e1000/if_em.h
@@ -267,6 +267,7 @@
 #define HW_DEBUGOUT2(S, A, B)       if (DEBUG_HW) printf(S "\n", A, B)
 
 #define EM_MAX_SCATTER		64
+#define EM_MAX_LEGACY_SCATTER	40
 #define EM_VFTA_SIZE		128
 #define EM_TSO_SIZE		(65535 + sizeof(struct ether_vlan_header))
 #define EM_TSO_SEG_SIZE		4096	/* Max dma segment size */
Index: sys/dev/e1000/if_em.c
===================================================================
--- sys/dev/e1000/if_em.c
+++ sys/dev/e1000/if_em.c
@@ -397,6 +397,10 @@
 SYSCTL_INT(_hw_em, OID_AUTO, txd, CTLFLAG_RDTUN, &em_txd, 0,
     "Number of transmit descriptors per queue");
 
+static int em_max_dma = EM_MAX_SCATTER;
+SYSCTL_INT(_hw_em, OID_AUTO, rxd, CTLFLAG_RDTUN, &em_max_dma 0,
+    "Maximum number of descriptors we allow to be pushed to the card");
+
 static int em_smart_pwr_down = FALSE;
 SYSCTL_INT(_hw_em, OID_AUTO, smart_pwr_down, CTLFLAG_RDTUN, &em_smart_pwr_down,
     0, "Set to true to leave smart power down enabled on newer adapters");
@@ -665,6 +669,15 @@
 	 */
 	hw->mac.report_tx_early = 1;
 
+	/*
+	 * If there is a known quirk for an Intel board
+	 * where it cannot handle a DMA of >40 mbufs, note
+	 * it here. sbruno 04FEB2016
+	 */
+	if (hw->mac.type == e1000_82573) {
+		if (em_max_dma > EM_MAX_LEGACY_SCATTER)
+			em_max_dma = EM_MAX_LEGACY_SCATTER;
+	}
 	/* 
 	** Get queue/ring memory
 	*/
@@ -954,7 +967,7 @@
         	/* Call cleanup if number of TX descriptors low */
 		if (txr->tx_avail <= EM_TX_CLEANUP_THRESHOLD)
 			em_txeof(txr);
-		if (txr->tx_avail < EM_MAX_SCATTER) {
+		if (txr->tx_avail < em_max_dma) {
 			if_setdrvflagbits(ifp,IFF_DRV_OACTIVE, 0);
 			break;
 		}
@@ -1080,9 +1093,9 @@
 	if ((enq > 0) && (txr->busy == EM_TX_IDLE))
 		txr->busy = EM_TX_BUSY;
 
-	if (txr->tx_avail < EM_MAX_SCATTER)
+	if (txr->tx_avail < em_max_dma)
 		em_txeof(txr);
-	if (txr->tx_avail < EM_MAX_SCATTER) {
+	if (txr->tx_avail < em_max_dma) {
 		if_setdrvflagbits(ifp, IFF_DRV_OACTIVE,0);
 	}
 	return (err);
@@ -1879,7 +1892,7 @@
 em_xmit(struct tx_ring *txr, struct mbuf **m_headp)
 {
 	struct adapter		*adapter = txr->adapter;
-	bus_dma_segment_t	segs[EM_MAX_SCATTER];
+	bus_dma_segment_t	segs[em_max_dma];
 	bus_dmamap_t		map;
 	struct em_txbuffer	*tx_buffer, *tx_buffer_mapped;
 	struct e1000_tx_desc	*ctxd = NULL;
@@ -2042,7 +2055,7 @@
 	if (error == EFBIG && remap) {
 		struct mbuf *m;
 
-		m = m_collapse(*m_headp, M_NOWAIT, EM_MAX_SCATTER);
+		m = m_collapse(*m_headp, M_NOWAIT, em_max_dma);
 		if (m == NULL) {
 			adapter->mbuf_defrag_failed++;
 			m_freem(*m_headp);
@@ -2073,7 +2086,7 @@
 		txr->tx_tso = FALSE;
 	}
 
-        if (nsegs > (txr->tx_avail - EM_MAX_SCATTER)) {
+        if (nsegs > (txr->tx_avail - em_max_dma)) {
                 txr->no_desc_avail++;
 		bus_dmamap_unload(txr->txtag, map);
 		return (ENOBUFS);
@@ -2325,7 +2338,7 @@
 		if (txr->busy >= EM_TX_MAXTRIES)
 			txr->busy = EM_TX_HUNG;
 		/* Schedule a TX tasklet if needed */
-		if (txr->tx_avail <= EM_MAX_SCATTER)
+		if (txr->tx_avail <= em_max_dma)
 			taskqueue_enqueue(txr->tq, &txr->tx_task);
 	}
 	
@@ -3054,7 +3067,7 @@
 	if_setgetcounterfn(ifp, em_get_counter);
 	/* TSO parameters */
 	ifp->if_hw_tsomax = IP_MAXPACKET;
-	ifp->if_hw_tsomaxsegcount = EM_MAX_SCATTER;
+	ifp->if_hw_tsomaxsegcount = em_max_dma;
 	ifp->if_hw_tsomaxsegsize = EM_TSO_SEG_SIZE;
 
 #ifdef EM_MULTIQUEUE
@@ -3378,7 +3391,7 @@
 			       BUS_SPACE_MAXADDR,	/* highaddr */
 			       NULL, NULL,		/* filter, filterarg */
 			       EM_TSO_SIZE,		/* maxsize */
-			       EM_MAX_SCATTER,		/* nsegments */
+			       em_max_dma,		/* nsegments */
 			       PAGE_SIZE,		/* maxsegsize */
 			       0,			/* flags */
 			       NULL,			/* lockfunc */
@@ -4038,7 +4051,7 @@
 	 * TX lock which, with a single queue, guarantees 
 	 * sanity.
          */
-        if (txr->tx_avail >= EM_MAX_SCATTER) {
+        if (txr->tx_avail >= em_max_dma) {
 		if_setdrvflagbits(ifp, 0, IFF_DRV_OACTIVE);
 	}